Project Summary Clinical or subclinical eating disorders (EDs) impact 10% of individuals in their lifetime and are marked by significant functional impairment, early mortality, chronicity, and emotional distress. ED symptoms often emerge in adolescence, with peak onset age in the teenage years. Early recognition and treatment of these devastating illnesses are needed to prevent long-term consequences and a chronic course. Most (80%) individuals with EDs, including teens with EDs (TwEDs), do not receive treatment. Due to major barriers to access and to the delivery of treatment for TwEDs, there is a need for a new model of service delivery that can identify and help TwEDs. We have studied ED-related networking on social media and have demonstrated our ability to harness social media, which is used ubiquitously among teens, to identify and efficiently recruit large numbers of TwEDs. At the same time, our team has successfully developed a guided self-help cognitive- behavioral therapy (CBT)-based mobile app, StudentBodies-Eating Disorders (SB-ED), which includes personalized coaching and interactive sessions to address key ED treatment targets and has demonstrated efficacy among college women with EDs. This tool has great potential to be adapted to address the specific needs of TwEDs. In Aim #1 of the proposed study, we will update and adapt SB-ED to create #ByeED for TwEDs by 1) simplifying language and making content relevant to adolescent issues, 2) including a rewards feature to motivate continued app use, 3) including a within-app social networking feature to facilitate group exchanges and coach-led weekly group sessions, and 4) harnessing machine learning to digest users? social networking data within #ByeED to respond to potential recovery setbacks in real-time and tailor coaching interactions. Following a small focus group of TwEDs to assess initial impressions of the app, #ByeED will be piloted among 20 TwEDs recruited from Instagram, garnering feedback via a mixed methods approach on the efficiency, technical effectiveness, and satisfaction with #ByeED. The app will be further refined for a small pilot randomized controlled trial (RCT) in Aim #2, where we will again leverage Instagram for recruitment of TwEDs who are not engaged in treatment. This RCT will approximate the preliminary effectiveness of #ByeED (n=50) versus a control group (encouraging in-person treatment in their communities, n=50) in reducing ED symptoms, improving quality of life, increasing uptake of care, and impacting targets that are associated with outcomes. We will explore within-app predictors of outcomes, potential moderators of treatment effects (e.g., psychiatric comorbidity), and participant perspectives on potential additional parental involvement in #ByeED. Effect size and attrition estimates will aid in the planning of a larger RCT (R01 mechanism) where we will further expand #ByeED (e.g., automated coaching, parental involvement) and test the app on a larger scale to improve its potential to reduce the extraordinary burden of EDs among teens.